How to group by AND aggregate with Django

问题

I have a fairly simple query I\'d like to make via the ORM, but can\'t figure that out..

I have three models:

Location (a place), Attribute (an attribute a place might have), and Rating (a M2M \'through\' model that also contains a score field)

I want to pick some important attributes and be able to rank my locations by those attributes - i.e. higher total score over all selected attributes = better.

I can use the following SQL to get what I want:

select location_id, sum(score) 
    from locations_rating 
    where attribute_id in (1,2,3) 
    group by location_id order by sum desc;

which returns

 location_id | sum 
-------------+-----
          21 |  12
           3 |  11

The closest I can get with the ORM is:

Rating.objects.filter(
    attribute__in=attributes).annotate(
    acount=Count(\'location\')).aggregate(Sum(\'score\'))

Which returns

{\'score__sum\': 23}

i.e. the sum of all, not grouped by location.

Any way around this? I could execute the SQL manually, but would rather go via the ORM to keep things consistent.

Thanks

回答1:

Try this:

Rating.objects.filter(attribute__in=attributes) \
    .values('location') \
    .annotate(score = Sum('score')) \
    .order_by('-score')

回答2:

Can you try this.

Rating.objects.values('location_id').filter(attribute__in=attributes).annotate(sum_score=Sum('score')).

来源：https://stackoverflow.com/questions/13403609/how-to-group-by-and-aggregate-with-django